Segment Information Total Segment Assets (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Segment Reporting Information
Total assets	$ 8,566	$ 8,123
Gathering and Processing
Segment Reporting Information
Total assets	4,631	4,210
Natural Gas Transportation
Segment Reporting Information
Total assets	1,005	1,232
NGL Services
Segment Reporting Information
Total assets	1,040	948
Contract Services [Member]
Segment Reporting Information
Total assets	1,812	1,672
Corporate and Others
Segment Reporting Information
Total assets	$ 78	$ 61